We will pursue experiments aimed at resolving the contributions of various host cell types in the antitumor action of C. parvum. Specifically, we will attempt to resolve the discrepancy between estimates of specific antitumor T cell activity in the spleen of tumor-bearing C. parvum-treated mice as determined by WINN assays or adoptive transfer assays. We will attempt to predict the tumors which will regress in response to C. parvum therapy on the basis of the early normal host cell infiltrate as measured by flow cytometry. In conjunction with these experiments, we will determine whether the sporadic occurrence of complete tumor regressions induced by systemic C. parvum is related to the host animal or to the microenvironment of the implanted tumor. We plan to continue our studies of the perturbations produced by irradiation and cytotoxic agents on both immunological and nonimmunological functions in an effort to elucidate the mechanisms of enhanced tumor transplantability and metastases resulting from these treatments.